mirror of
https://github.com/apache/commons-math.git
synced 2025-02-08 02:59:36 +00:00
[MATH-777] added NPointCrossover policy, thanks to Reid Hochstedler.
git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1344030 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Thomas Neidhart
parent
129e53d466
commit
86e1cc0335
@ -0,0 +1,178 @@
|
||||
/*
|
||||
* Licensed to the Apache Software Foundation (ASF) under one or more
|
||||
* contributor license agreements. See the NOTICE file distributed with
|
||||
* this work for additional information regarding copyright ownership.
|
||||
* The ASF licenses this file to You under the Apache License, Version 2.0
|
||||
* (the "License"); you may not use this file except in compliance with
|
||||
* the License. You may obtain a copy of the License at
|
||||
*
|
||||
* http://www.apache.org/licenses/LICENSE-2.0
|
||||
*
|
||||
* Unless required by applicable law or agreed to in writing, software
|
||||
* distributed under the License is distributed on an "AS IS" BASIS,
|
||||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
||||
* See the License for the specific language governing permissions and
|
||||
* limitations under the License.
|
||||
*/
|
||||
package org.apache.commons.math3.genetics;
|
||||
|
||||
import java.util.ArrayList;
|
||||
import java.util.List;
|
||||
|
||||
import org.apache.commons.math3.exception.DimensionMismatchException;
|
||||
import org.apache.commons.math3.exception.MathIllegalArgumentException;
|
||||
import org.apache.commons.math3.exception.NotStrictlyPositiveException;
|
||||
import org.apache.commons.math3.exception.NumberIsTooLargeException;
|
||||
import org.apache.commons.math3.exception.util.LocalizedFormats;
|
||||
import org.apache.commons.math3.random.RandomGenerator;
|
||||
|
||||
/**
|
||||
* N-point crossover policy. For each iteration a random crossover point is
|
||||
* selected and the first part from each parent is copied to the corresponding
|
||||
* child, and the second parts are copied crosswise.
|
||||
*
|
||||
* Example (2-point crossover):
|
||||
* <pre>
|
||||
* -C- denotes a crossover point
|
||||
* -C- -C- -C- -C-
|
||||
* p1 = (1 0 | 1 0 0 1 | 0 1 1) X p2 = (0 1 | 1 0 1 0 | 1 1 1)
|
||||
* \----/ \-------/ \-----/ \----/ \--------/ \-----/
|
||||
* || (*) || || (**) ||
|
||||
* VV (**) VV VV (*) VV
|
||||
* /----\ /--------\ /-----\ /----\ /--------\ /-----\
|
||||
* c1 = (1 0 | 1 0 1 0 | 0 1 1) X c2 = (0 1 | 1 0 0 1 | 0 1 1)
|
||||
* </pre>
|
||||
*
|
||||
* This policy works only on {@link AbstractListChromosome}, and therefore it
|
||||
* is parameterized by T. Moreover, the chromosomes must have same lengths.
|
||||
*
|
||||
* @param <T> generic type of the {@link AbstractListChromosome}s for crossover
|
||||
* @since 3.1
|
||||
* @version $Id$
|
||||
*/
|
||||
public class NPointCrossover<T> implements CrossoverPolicy {
|
||||
|
||||
/** The number of crossover points. */
|
||||
private final int crossoverPoints;
|
||||
|
||||
/**
|
||||
* Creates a new {@link NPointCrossover} policy using the given number of points.
|
||||
*
|
||||
* <p><b>Note</b>: the number of crossover points must be < <code>chromosome length - 1</code>.
|
||||
* This condition can only be checked at runtime, as the chromosome length is not known in advance.
|
||||
* </p>
|
||||
*
|
||||
* @param crossoverPoints the number of crossover points
|
||||
* @throws NotStrictlyPositiveException if the number of {@code crossoverPoints} is not
|
||||
* strictly positive
|
||||
*/
|
||||
public NPointCrossover(final int crossoverPoints) {
|
||||
if (crossoverPoints <= 0) {
|
||||
throw new NotStrictlyPositiveException(crossoverPoints);
|
||||
}
|
||||
this.crossoverPoints = crossoverPoints;
|
||||
}
|
||||
|
||||
/**
|
||||
* Returns the number of crossover points used by this {@link CrossoverPolicy}.
|
||||
*
|
||||
* @return the number of crossover points
|
||||
*/
|
||||
public int getCrossoverPoints() {
|
||||
return crossoverPoints;
|
||||
}
|
||||
|
||||
/**
|
||||
* Performs a N-point crossover. N random crossover points are selected and are used
|
||||
* to divide the parent chromosomes into segments. The segments are copied in alternate
|
||||
* order from the two parents to the corresponding child chromosomes.
|
||||
*
|
||||
* Example (2-point crossover):
|
||||
* <pre>
|
||||
* -C- denotes a crossover point
|
||||
* -C- -C- -C- -C-
|
||||
* p1 = (1 0 | 1 0 0 1 | 0 1 1) X p2 = (0 1 | 1 0 1 0 | 1 1 1)
|
||||
* \----/ \-------/ \-----/ \----/ \--------/ \-----/
|
||||
* || (*) || || (**) ||
|
||||
* VV (**) VV VV (*) VV
|
||||
* /----\ /--------\ /-----\ /----\ /--------\ /-----\
|
||||
* c1 = (1 0 | 1 0 1 0 | 0 1 1) X c2 = (0 1 | 1 0 0 1 | 0 1 1)
|
||||
* </pre>
|
||||
*
|
||||
* @param first first parent (p1)
|
||||
* @param second second parent (p2)
|
||||
* @return pair of two children (c1,c2)
|
||||
* @throws MathIllegalArgumentException iff one of the chromosomes is
|
||||
* not an instance of {@link AbstractListChromosome}
|
||||
* @throws DimensionMismatchException if the length of the two chromosomes is different
|
||||
*/
|
||||
@SuppressWarnings("unchecked") // OK because of instanceof checks
|
||||
public ChromosomePair crossover(final Chromosome first, final Chromosome second) {
|
||||
if (!(first instanceof AbstractListChromosome<?> && second instanceof AbstractListChromosome<?>)) {
|
||||
throw new MathIllegalArgumentException(LocalizedFormats.INVALID_FIXED_LENGTH_CHROMOSOME);
|
||||
}
|
||||
return mate((AbstractListChromosome<T>) first, (AbstractListChromosome<T>) second);
|
||||
}
|
||||
|
||||
/**
|
||||
* Helper for {@link #crossover(Chromosome, Chromosome)}. Performs the actual crossover.
|
||||
*
|
||||
* @param first the first chromosome
|
||||
* @param second the second chromosome
|
||||
* @return the pair of new chromosomes that resulted from the crossover
|
||||
* @throws DimensionMismatchException if the length of the two chromosomes is different
|
||||
* @throws NumberIsTooLargeException if the number of crossoverPoints is too large for the
|
||||
* actual chromosomes
|
||||
*/
|
||||
private ChromosomePair mate(final AbstractListChromosome<T> first,
|
||||
final AbstractListChromosome<T> second) {
|
||||
final int length = first.getLength();
|
||||
if (length != second.getLength()) {
|
||||
throw new DimensionMismatchException(second.getLength(), length);
|
||||
}
|
||||
if (crossoverPoints >= length) {
|
||||
throw new NumberIsTooLargeException(crossoverPoints, length, false);
|
||||
}
|
||||
|
||||
// array representations of the parents
|
||||
final List<T> parent1Rep = first.getRepresentation();
|
||||
final List<T> parent2Rep = second.getRepresentation();
|
||||
// and of the children
|
||||
final ArrayList<T> child1Rep = new ArrayList<T>(first.getLength());
|
||||
final ArrayList<T> child2Rep = new ArrayList<T>(second.getLength());
|
||||
|
||||
final RandomGenerator random = GeneticAlgorithm.getRandomGenerator();
|
||||
|
||||
ArrayList<T> c1 = child1Rep;
|
||||
ArrayList<T> c2 = child2Rep;
|
||||
|
||||
int remainingPoints = crossoverPoints;
|
||||
int lastIndex = 0;
|
||||
for (int i = 0; i < crossoverPoints; i++, remainingPoints--) {
|
||||
// select the next crossover point at random
|
||||
final int crossoverIndex = 1 + lastIndex + random.nextInt(length - lastIndex - remainingPoints);
|
||||
|
||||
// copy the current segment
|
||||
for (int j = lastIndex; j < crossoverIndex; j++) {
|
||||
c1.add(parent1Rep.get(j));
|
||||
c2.add(parent2Rep.get(j));
|
||||
}
|
||||
|
||||
// swap the children for the next segment
|
||||
ArrayList<T> tmp = c1;
|
||||
c1 = c2;
|
||||
c2 = tmp;
|
||||
|
||||
lastIndex = crossoverIndex;
|
||||
}
|
||||
|
||||
// copy the last segment
|
||||
for (int j = lastIndex; j < length; j++) {
|
||||
c1.add(parent1Rep.get(j));
|
||||
c2.add(parent2Rep.get(j));
|
||||
}
|
||||
|
||||
return new ChromosomePair(first.newFixedLengthChromosome(child1Rep),
|
||||
second.newFixedLengthChromosome(child2Rep));
|
||||
}
|
||||
}
|
||||
@ -0,0 +1,113 @@
|
||||
package org.apache.commons.math3.genetics;
|
||||
|
||||
import java.util.List;
|
||||
|
||||
import org.apache.commons.math3.exception.DimensionMismatchException;
|
||||
import org.apache.commons.math3.exception.MathIllegalArgumentException;
|
||||
import org.apache.commons.math3.exception.NumberIsTooLargeException;
|
||||
import org.junit.Assert;
|
||||
import org.junit.Test;
|
||||
|
||||
public class NPointCrossoverTest {
|
||||
|
||||
@Test(expected = DimensionMismatchException.class)
|
||||
public void testCrossoverDimensionMismatchException() {
|
||||
final Integer[] p1 = new Integer[] {1,0,1,0,0,1,0,1,1};
|
||||
final Integer[] p2 = new Integer[] {0,1,1,0,1};
|
||||
|
||||
final BinaryChromosome p1c = new DummyBinaryChromosome(p1);
|
||||
final BinaryChromosome p2c = new DummyBinaryChromosome(p2);
|
||||
|
||||
final CrossoverPolicy cp = new NPointCrossover<Integer>(1);
|
||||
cp.crossover(p1c,p2c);
|
||||
}
|
||||
|
||||
@Test(expected = NumberIsTooLargeException.class)
|
||||
public void testNumberIsTooLargeException() {
|
||||
final Integer[] p1 = new Integer[] {1,0,1,0,0,1,0,1,1};
|
||||
final Integer[] p2 = new Integer[] {0,1,1,0,1,0,1,1,1};
|
||||
|
||||
final BinaryChromosome p1c = new DummyBinaryChromosome(p1);
|
||||
final BinaryChromosome p2c = new DummyBinaryChromosome(p2);
|
||||
|
||||
final CrossoverPolicy cp = new NPointCrossover<Integer>(15);
|
||||
cp.crossover(p1c,p2c);
|
||||
}
|
||||
|
||||
@Test(expected = MathIllegalArgumentException.class)
|
||||
public void testCrossoverInvalidFixedLengthChromosomeFirst() {
|
||||
final Integer[] p1 = new Integer[] {1,0,1,0,0,1,0,1,1};
|
||||
final BinaryChromosome p1c = new DummyBinaryChromosome(p1);
|
||||
final Chromosome p2c = new Chromosome() {
|
||||
public double fitness() {
|
||||
// Not important
|
||||
return 0;
|
||||
}
|
||||
};
|
||||
|
||||
final CrossoverPolicy cp = new NPointCrossover<Integer>(1);
|
||||
cp.crossover(p1c,p2c);
|
||||
}
|
||||
|
||||
@Test(expected = MathIllegalArgumentException.class)
|
||||
public void testCrossoverInvalidFixedLengthChromosomeSecond() {
|
||||
final Integer[] p1 = new Integer[] {1,0,1,0,0,1,0,1,1};
|
||||
final BinaryChromosome p2c = new DummyBinaryChromosome(p1);
|
||||
final Chromosome p1c = new Chromosome() {
|
||||
public double fitness() {
|
||||
// Not important
|
||||
return 0;
|
||||
}
|
||||
};
|
||||
|
||||
final CrossoverPolicy cp = new NPointCrossover<Integer>(1);
|
||||
cp.crossover(p1c,p2c);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void testCrossover() {
|
||||
Integer[] p1 = new Integer[] {1,0,1,0,1,0,1,0,1};
|
||||
Integer[] p2 = new Integer[] {0,1,0,1,0,1,0,1,0};
|
||||
|
||||
BinaryChromosome p1c = new DummyBinaryChromosome(p1);
|
||||
BinaryChromosome p2c = new DummyBinaryChromosome(p2);
|
||||
|
||||
final int order = 3;
|
||||
NPointCrossover<Integer> npc = new NPointCrossover<Integer>(order);
|
||||
|
||||
// the two parent chromosomes are different at each position, so it is easy to detect
|
||||
// the number of crossovers that happened for each child
|
||||
for (int i=0; i<20; i++) {
|
||||
ChromosomePair pair = npc.crossover(p1c,p2c);
|
||||
|
||||
Integer[] c1 = new Integer[p1.length];
|
||||
Integer[] c2 = new Integer[p2.length];
|
||||
|
||||
c1 = ((BinaryChromosome) pair.getFirst()).getRepresentation().toArray(c1);
|
||||
c2 = ((BinaryChromosome) pair.getSecond()).getRepresentation().toArray(c2);
|
||||
|
||||
Assert.assertEquals(order, detectCrossoverPoints(p1c, p2c, (BinaryChromosome) pair.getFirst()));
|
||||
Assert.assertEquals(order, detectCrossoverPoints(p2c, p1c, (BinaryChromosome) pair.getSecond()));
|
||||
}
|
||||
}
|
||||
|
||||
private int detectCrossoverPoints(BinaryChromosome p1, BinaryChromosome p2, BinaryChromosome c) {
|
||||
int crossovers = 0;
|
||||
final int length = p1.getLength();
|
||||
|
||||
final List<Integer> p1Rep = p1.getRepresentation();
|
||||
final List<Integer> p2Rep = p2.getRepresentation();
|
||||
final List<Integer> cRep = c.getRepresentation();
|
||||
|
||||
List<Integer> rep = p1Rep;
|
||||
for (int i = 0; i < length; i++) {
|
||||
if (rep.get(i) != cRep.get(i)) {
|
||||
crossovers++;
|
||||
rep = rep == p1Rep ? p2Rep : p1Rep;
|
||||
}
|
||||
}
|
||||
|
||||
return crossovers;
|
||||
}
|
||||
|
||||
}
|
||||
Loading…
x
Reference in New Issue
Block a user